Influenza virus infects 5-20% of the population and results in 30,000-50,000 deaths each year in the U.S. Although the influenza vaccine is the primary method of infection prevention, four antiviral drugs are also available in the U.S.: amantadine, rimantadine, oseltamivir and zanamivir. As of December 2005, only oseltamivir (TAMIFLU™) is recommended for treatment of influenza A due to the increasing resistance of the virus to amantadine and rimantidine resulting from an amino acid substitution in the M2 protein of the virus.
Disease caused by influenza A viral infections is typified by its cyclical nature. Antigenic drift and shift allow for different A strains to emerge every year. Added to that, the threat of highly pathogenic strains entering into the general population has stressed the need for novel therapies for flu infections. The predominant fraction of neutralizing antibodies is directed to the polymorphic regions of the hemagglutinin and neuraminidase proteins. Thus, such a neutralizing MAb would presumably target only one or a few strains. A recent focus has been on the relatively invariant matrix 2 (M2) protein. Potentially, a neutralizing MAb to M2 would be an adequate therapy for all influenza A strains.
The M2 protein is found in a homotetramer that forms an ion channel and is thought to aid in the uncoating of the virus upon entering the cell. After infection, M2 can be found in abundance at the cell surface. It is subsequently incorporated into the virion coat, where it only comprises about 2% of total coat protein. The M2 extracellular domain (M2e) is short, with the aminoterminal 2-24 amino acids displayed outside of the cell. Anti-M2 MAbs to date have been directed towards this linear sequence. Thus, they may not exhibit desired binding properties to cellularly expressed M2, including conformational determinants on native M2.
Therefore, a long-felt need exists in the art for new antibodies that bind to the cell-expressed M2 and conformational determinants on the native M2.